1. Field of the Invention
The present invention relates to an engine generator apparatus and in particular, to an engine generator apparatus provided with a purifier of engine exhaust.
2. Description of the Related Art
In recent years, there has been a widespread use of compact generator apparatus capable of being easily installed relatively. Further, there are indications that a widespread use of co-generation type engine generator apparatus that not only generate electric power but also utilize exhaust heat generated when an engine for generating electric power is operated to enhance operation efficiency. A study of reducing the physical size of this type of engine generator apparatus for domestic use has been also conducted.
In this kind of generator apparatus, in order to give special considerations to atmospheric environment, for example, in a case where a generator driven by a gasoline engine or a gas engine is used, the air-fuel ratio of an air-fuel mixture supplied to the engine is controlled to a theoretical air-fuel ratio to purify exhaust gas.
In the above-mentioned control of an air-fuel ratio, an oxygen sensor with which the oxygen density is sensed is provided in the exhaust passage of the engine needs to be kept at a temperature in which the sensor can stably operate, that is, a temperature for activating the sensor (for example, 400° C.). An exhaust temperature and an exhaust speed also have an effect on the temperature for activating the sensor, so usually, an engine revolution speed range and a throttle opening (or a fuel injection quantity) range are previously set such that the senor is operated within a predetermined operating zone calculated from these ranges.
In a case where the engine is operated almost at a constant speed, the operating zone of the oxygen sensor is not required to be set: for example, in the above engine generator apparatus, in a case where the engine is operated almost at a constant speed of increasing operation efficiency by the use of a governor of the number of revolutions.
However, if the revolution speed of the engine is set almost at a constant speed in the engine generator apparatus, when an electric load is eliminated or extremely reduced, the range of variation in the number of revolutions of the engine increases, so the detection signal of the oxygen sensor is likely to become unstable.
One example of an engine generator apparatus in which an electric load is varied is that the engine generator apparatus is interconnected to a power network or grid (for example, Japanese Unexamined Patent Publication No. 2002-70607). In this example, when the engine generator apparatus is released from the power network because of power failure, the load is also isolated at the same time to bring the engine generator apparatus into a no-load operation to increase variation in the number of revolutions, which is likely to cause an unstable output of the oxygen sensor.